echo o/n
read x 
until [  $x = "n" ]
do
case $x in 
o*)
echo entrez l operateur 
read o
echo entrez l operant 1
read a
echo entrez l operant 2 
read b
echo le resultat est : 
t=` expr $a $o $b `
echo $t
echo une autre operation? o/n/l
;;
l*)
echo entrez l operateur 
read o
echo entrez l operant 1
read a
echo le resultat est : 
t=` expr $t $o $a `
echo $t
;;
esac
read x
done 

